The present invention regards systems and processes for measuring displacement of a surface using photography.
There have been numerous studies of strain or displacement estimation using image processing but none that propose the combination of specific oblique camera placement (wherein the optical axis of the camera lens is positioned oblique to the surface plane) and image processing as a key element for measuring displacement of a free surface. Typically, studies have combined normal incident photos of material cross-sections and digital processing to measure compressive and tensile strain inside the material.
Typical practice for using photography to measure changes in surface topography, such as the displacement of a surface, generally employ photogrammetric techniques to construct digital three dimensional (3D) models representing ‘before’ and ‘after’ conditions of the surface under investigation, and then perform a subtraction of ‘before’ and ‘after’ surface coordinates to determine the change. These techniques are applicable to a broad range of surface shapes and are robust, but they have the disadvantage that photogrammetric construction of 3D models requires multiple images from multiple camera poses to construct each model, causing processing to be computationally intensive and thus time-consuming. Further, when assessing small displacements in relatively rough surfaces, errors introduced by sampling surface features from multiple angles may be large relative to the displacement of interest.
The systems and processes of the present invention provide a more accurate, less computationally intensive, faster process for measuring displacement of a surface, requiring fewer image samples than prior approaches. In addition, the present invention is less sensitive to signal-to-noise issues in measuring small average displacements over a rough surface.